COGS 17 Lecture Notes - Lecture 8: Ossicles, Tectorial Membrane, Basilar Membrane
Lec 5A - Audition
● Sound waves
● Frequency = number of cycles/second (Hz)
○ Per speed at which molecules of medium (air) oscillate
● Phase = place in cycle of condensation and rarefaction
○ Peak and trough
● Amplitude = distance a given molecule of medium (air) travels during its
oscillation
● Auditory reception
○ Pinna - external ear. Individually distinct as fingerprints
○ Auditory canal ends in eardrum
○ Eardrum - thin membrane, also called tympanic membrane
○ Ossicles - smallest bones, libra system leads to cochlea
○ Cochlea - neurons that react to vibration in ear
● The middle ear
○ Eardrum - connects to auditory ossicles (bones): malleus, incus, and
stapes
■ Jointed together
■ Malleus pushed up against tympanic membrane
■ Stapes up against the oval window (membrane) - much
smaller than tympanic
■ Ossicles function is to convert large vibrations of big tympanic
membrane into smaller, but more powerful vibrations of oval
window
● Overcomes impedance (resistance that a medium puts
up to propagate sound) mismatch between air and
cochlear fluid inside the cochlea
● Vibrations
○ The cochlea
■ Coiled into a snail shape
■ Upper, lower and middle chamber
■ Middle chamber → organ of corti
● Where neurons are that react to vibrations in ear
● Basilar membrane: floor of middle chamber and organ
of corti, on which the hair cells (receptors) sit
● Tectorial membrane: within the middle chamber, top of
organ of corti
○ Organ of corti
■ Hair cells - auditory receptors
● Stand between tectorial membrane above, and basilar
membrane blow
● As membranes vibrate, cilia (hairs) are bent → release
NT
■ Transduction in hair cells is potassium (K+) based (no Na+)
● Cochlear fluid is rich in potassium
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Document Summary
Per speed at which molecules of medium (air) oscillate. Phase = place in cycle of condensation and rarefaction. Amplitude = distance a given molecule of medium (air) travels during its oscillation. Eardrum - thin membrane, also called tympanic membrane. Ossicles - smallest bones, libra system leads to cochlea. Cochlea - neurons that react to vibration in ear. Eardrum - connects to auditory ossicles (bones): malleus, incus, and stapes. Stapes up against the oval window (membrane) - much smaller than tympanic. Ossicles function is to convert large vibrations of big tympanic membrane into smaller, but more powerful vibrations of oval window. Overcomes impedance (resistance that a medium puts up to propagate sound) mismatch between air and cochlear fluid inside the cochlea. Where neurons are that react to vibrations in ear. Basilar membrane: floor of middle chamber and organ of corti, on which the hair cells (receptors) sit. Tectorial membrane: within the middle chamber, top of organ of corti.